Laminated magnetic core for electric machines

ABSTRACT

The present invention relates to a laminated magnetic core for rotating electric machines. The laminated magnetic core comprises a number of stack members ( 40 ), each consisting of a number of sheets of metal joined together. Each stack member ( 40 ) is provided with two identical grooves ( 42 ) arranged to cooperate with wedge members ( 46 ) designed to join the stack members ( 40 ). The cross-sectional area of the groove ( 42 ) is larger than the cross-sectional area of the wedge member ( 46 ) and the wedge member ( 46 ) has two protrusions arranged symmetrically in relation to the longitudinal axis of the wedge member. The groove ( 42 ) has at least one part shaped to fit said protrusion. The stack members ( 40 ) in the laminated magnetic core are stacked on and partially overlapping each other to form different layers of stack members ( 40 ). The grooves ( 42 ) in the stack members ( 40 ) in the various layers are arranged substantially opposite each other with the wedge members ( 46 ) arranged in the grooves ( 42 ) and a protrusion abutting the complementary shape of the groove ( 42 ) in such a manner that the stack members ( 40 ) in one layer are secured counter-clockwise in tangential direction and that the stack members in at least one of the adjacent layers are secured clockwise in tangential direction. The laminated magnetic core also includes locking members arranged at least at the transition between layers secured clockwise and layers secured counter-clockwise in order to prevent tangential movement between the different layers.

TECHNICAL FIELD

The present invention relates to a laminated magnetic core for rotatingelectric machines and a rotating electric machine comprising suchlaminated magnetic core.

The machine is in the first place intended as a generator in a powerstation for generating electric power.

The invention is applicable to rotating electric machines such assynchronous machines and normal asynchronous machines. The invention isalso applicable to other electric machines such as dual-fed machines andapplications in synchronous static current converter cascades, outerpolemachines and synchronous flow machines provided their windings aremanufactured with insulating electric conductors, and preferably forhigh voltages. High voltages shall be understood here to mean electricvoltages in excess of 10 kV.

BACKGROUND ART

Similar machines have conventionally been designed for voltages in therange 15-30 kV, and 30 kV has normally been considered to be an upperlimit. This usually means that a generator must be connected to thepower network via a transformer which steps up the voltage to the levelof the power network—in the range of approximately 130-400 kV.

A machine which can operate at higher power levels and which can bedirectly connected to a power network is known from PCT/SE97/00874.

The laminations in laminated stator cores (laminated magnetic cores) forlarge electric machines are normally laid one by one with overlap insuch a way that grooves in the laminations match facing surfaces in thedovetail-shaped wedge of the stator frame. (See FIG. 2.) To enable thelamination to assume its position it is bent sufficiently for thedovetail-shaped groove part to pass the surface of the dovetail-shapedwedge. This method of manufacture is relatively complicated,time-consuming and thus expensive.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the problems mentionedabove. This is achieved with a laminated magnetic core for rotatingelectric machines as defined in claim 1, and a rotating electric machinecomprising a laminated magnetic core of the type described above asdefined in claim 10. The laminated magnetic core according to thepresent invention comprises a number of stack members, each consistingof a number of sheets of metal joined together. Each stack member isprovided with two identical grooves arranged to cooperate with wedgemembers designed to join the stack members together. Each wedge memberhas two protrusions arranged symmetrically in relation to thelongitudinal axis of the wedge member. Each groove in the stack memberhas at least one part shaped to fit said protrusion. The stack membersin the laminated magnetic core are stacked on and partially overlappingeach other to form different layers of stack members, the grooves in thestack members in the various layers being arranged substantiallyopposite each other. The wedge members are arranged in the grooves witha protrusion abutting the complementary shape of the groove in such amanner that the stack members in one layer are secured counter-clockwisein tangential direction and that the stack members in at least one ofthe adjacent layers are secured clockwise in tangential direction. Thelaminated magnetic core also includes locking members arranged at leastat the transition between layers secured clockwise and layers securedcounter-clockwise in order to prevent tangential movement between thedifferent layers.

The above-mentioned laminated magnetic core according to the presentinvention is easy and quick to manufacture. It is thus also relativelyinexpensive to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the followingdescription of preferred embodiments thereof, with reference to theaccompanying drawings in which

FIG. 1 shows a cross-sectional view of a high-voltage cable;

FIG. 2 shows a side view of a sheet of metal and a part of a wedgemember according to the state of the art, which is included in alaminated magnetic core according to the state of the art;

FIG. 3 shows a basic diagram explaining how the various sheets of metalare joined in relation to each other in a laminated magnetic coreaccording to the state of the art;

FIG. 4 shows a side view of a stack member and a part of wedge membersincluded in a laminated magnetic core according to a first embodiment ofthe present invention;

FIG. 5 shows a side view on an enlarged scale of how stack members indifferent layers are joined together by means of the wedge member in alaminated magnetic core according to the first embodiment of the presentinvention;

FIG. 6 shows a side view of a laminated magnetic core according to thepresent invention; and

FIG. 7 shows a side view on an enlarged scale of how stack members indifferent layers are joined together by means of the wedge member in alaminated magnetic core according to a second embodiment of the presentinvention.

FIG. 8 shows a side view of a stack member according to an alternativeembodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION:

FIG. 1 shows a cross-sectional view of a high-voltage cable 10 which istraditionally used for conducting electric power. The high-voltage cable10 may be a standard PEX-cable 145 kV but without sheath or screen. Thehigh-voltage cable 10 comprises an electric conductor that may consistof one or more strand parts 12 made of copper (Cu), for instance, andhaving circular cross section. These strand parts 12 are arranged in themiddle of the high-voltage cable 10. Around the strand parts 12 is afirst semiconducting layer 14, Around the first semiconducting layer 14is a first insulating layer 16, e.g. PEX insulation. Around the firstinsulating layer 16 is a second semiconducting layer 18.

FIG. 2 shows a side view of a sheet of metal 20 and a part of a wedgemember 22 according to the state of the art included in a laminatedmagnetic core according to the state of the art. Each sheet of metal 20is normally 0.35-0.50 mm thick and is provided with two grooves 24arranged along the outer long side of the sheet 20. As can be seen inFIG. 2, the inner and outer long sides of the sheet 20 have differentradii or curvature so that when the sheets 20 are fitted together toform a laminated magnetic core it will be cylindrical. The sheets 20 arealso provided with a number of slots 26 arranged along the inner longside. These slots 26 are intended for stator windings in the assembledlaminated magnetic core. The wedge members 22 (only a part of one wedgemember 22 is shown) are arranged on the stator frame (not shown) andhave a dovetail-shaped cross section at the end shown. The grooves 24arranged along the outer long side of the metal sheet 20 have aninclined flank 28 and a straight, perpendicular flank 30. As can be seenin FIG. 2 both the inclined flanks 28 of the grooves 24 in each metalsheet 20 face each other. When the metal sheets 20 are to be assembledto form a laminated magnetic core, they are applied one by one andpartially overlapping each other (see FIG. 3). The wedge members 22 arepermanently arranged on the stator frame and have a length in adirection perpendicular to the drawing that is equal to the length ofthe laminated magnetic core. To enable a metal sheet 20 to assumes itsproper position the metal sheet 20 must be bent so far that the inclinedflanks 28 of the grooves 24 can pass the dovetail-shaped surfaces of themember 22. This means that the inclined flanges 28 of the metal sheet 20match facing surfaces of the dovetail-shaped wedge member 22.

FIG. 3 shows a basic diagram explaining how the different metal sheetsare joined in relation to each other in a laminated magnetic coreaccording to the state of the art. The sheets and wedges used may be asshown in FIG. 2, for instance. FIG. 3 shows four laminations 20′, 20″,20′″, 20″″ where the sheets 20′ and 20″ are arranged in the lower layerand the sheets 20′″ and 20″″ are arranged in the upper layer. As can beseen in FIG. 3, the sheets 20′ and 20′″ are arranged partiallyoverlapping so that one and the same wedge member (not shown, butintimated at 32′) is arranged in the right groove of the sheet 20′ andin the left groove of the sheet 20′″. In corresponding manner the sheets20″ and 20′″ are assembled partially overlapping so that one and thesame wedge member (not shown, but intimated at 32″) is arranged in theright groove of the sheet 20′″ and in the left groove of the sheet 20′.The laminations are thus assembled one by one in order to produce alaminated magnetic core according to the state of the art. As pointedout in connection with FIG. 2, each lamination must be bent sufficientlyto allow assembly.

FIG. 4 shows a side view of a stack member and a part of wedge membersin a laminated magnetic core according to a first embodiment of thepresent invention. Each stack member 40 comprises a number of metalsheets joined together. The metal sheets may have a thickness of0.35-0.50 mm, for instance. Each stack member 40 comprises 50-100sheets, for instance, which have been glued together. Each stack member40 comprises two identical grooves 42 arranged along the outer long sideof the stack member 40. As can be seen in FIG. 4, the inner and outerlong sides of the stack member 40 have different radii of curvature sothat when the stack members 40 are assembled to a laminated magneticcore it will be cylindrical. The stack members 40 are also provided witha number of slots 44 arranged along the inner long side of the stackmember 40. These slots 44 are intended for the stator windings in theassembled laminated magnetic core. The laminated magnetic core alsocomprises wedge members 46 (shown only partially) which are arranged onthe stator frame (not shown) and have a dovetailshaped cross section atthe end shown (see also FIG. 5). The grooves 42 arranged along the outerlong side of the stack member 40 have an inclined flank 48 and astraight, perpendicular flank 50. As can be seen in FIG. 4, both theinclined flanks 48 face the same way, i.e. they do not face each otheras is the case with the lamination shown in FIG. 2. Furthermore, theentrance of the groove 42 is wider than the greatest width of the wedgemember 46. This is shown even more clearly in FIG. 5. The main reasonfor the grooves 42 being shaped like this is that the stack members,comprising 50-100 laminations glued together, cannot be bent as is thecase with individual laminations according to FIG. 2. When assembling alaminated magnetic core a stack member 40 is positioned by the two wedgemembers 46 being inserted into the grooves 42, after which the stackmember 40 is displaced to the right in this case so that the inclinedflanks 48 abut the dovetail shape of the wedge member. This stack member40 is thus secured against clockwise movement in tangential direction.The next, partially overlapping stack member 40′ (see FIGS. 5 and 6) tobe assembled is first mirror-inverted so that the inclined flanges 48′of the grooves 42′ are on the right instead of the left side of thegrooves 42, 42′. Thereafter the mirror-inverted stack member ispositioned by inserting the two wedge members 46 into the grooves 42′,after which the stack member is displaced to the left in this case sothat the inclined flanks 48′ abut the dovetail shape of the wedgemembers 46. This stack member 40′ is thus secured againstcounter-clockwise movement in tangential direction. The arrangement of alocking member at the transition between the stack members 40 and 40′ inthis position, causes these stack members 40 and 40′ to be securedagainst tangential movement in both directions. This locking member mayconsist of a spot weld. (See FIG. 6.)

FIG. 6 shows a side view of a laminated magnetic core in accordance withthe invention. As can be seen in FIG. 6 the stack members are arrangedin different layers and partially overlapping like bricks in a wall, forinstance. The stack members in alternative layers are indicated byreference designations 40 and the stack members in the other layers areindicated by reference designations 40′. This means that the stackmembers 40′ are mirror-inverted in relation to the stack members 40. Italso means that all stack members 40 are secured againstcounter-clockwise movement in tangential direction thanks to beinglocked against the wedge members. This is indicated by the arrow A inFIG. 6. The stack members 40′, on the other hand, are secured againstclockwise movement in tangential direction, thanks to their being lockedagainst the wedge members. This is indicated by the arrow B in FIG. 6.If now locking members 52 in the form of spot welds 52 are arranged atat least alternate transitions between stack members 40 secured againstcounter-clockwise movement in tangential direction and stack members 40′secured against clockwise movement in tangential direction, tangentialmovement is prevented between the different layers. One variant is toarrange a linear weld instead of these spot welds 52.

The grooves in the stack members intended for the wedge member need nothave the cross section illustrated. The grooves may also have dovetailshape and still provide a similar function to that described inconnection with FIGS. 4-6. If dovetail-shaped grooves are used the stackmembers in alternate layers need not be mirror-inverted. On the otherhand, different stack members must be made for each layer. This isbecause, when the laminated magnetic core is assembled the slots 44 forthe stator windings must coincide. The slots 44 cannot therefore bearranged in the same way for stack members intended for differentlayers.

FIG. 7 shows a side view on an enlarged scale of how stack members indifferent layers are joined together by means of the wedge member in alaminated magnetic core according to a second embodiment of the presentinvention. As can be seen in FIG. 7 the wedge member 70 does not have adovetail-shaped cross section, but two protrusions 72 arrangedsymmetrically in relation to the longitudinal axis of the wedge member70. In this example the cross section of the protrusion 72 is in theshape of a semi-circle. FIG. 7 also shows part of a stack member 74located in one layer and a stack member 74′ located in an adjacentlayer. Each stack member 74, 74′ is provided with two grooves 76, 76′(only one groove is shown in the Figure) in a corresponding manner tothe embodiment shown in FIGS. 4-5. The grooves 76, 76′ have a part inthe form of a recess 78, 78′ with a form that fits the protrusion 72 onthe wedge member 70. In this example the cross-sectional shape of therecess 78, 78′ is a semi-circle. The grooves 76, 76′ are then defined bya straight, perpendicular flank 80, 80. As can be seen in FIG. 7 theentrance to the grooves 76, 76′ is larger than the greatest width of thecross section of the wedge member 70. The recess 78 of the groove 76 inthe stack member 74 abuts the left-hand protrusion 72 of the wedgemember 70 and secures the stack member 74 against clockwise movement intangential direction. The recess 78′ of the groove 76′ in the stackmember 74′ abuts the right-hand protrusion 72 of the wedge member 70 andsecures the stack member 74′ against counter-clockwise movement intangential direction. By applying a spot weld (not shown) in a mannercorresponding to that described with reference to FIG. 6, the stackmembers 74, 74′ are secured against tangential movement in bothdirections.

The cross sections of the recess of the wedge member and of the groovesintended for the wedge member need not be limited to the embodimentsshown. The protrusion on the wedge member may be rectangular, forinstance. The important thing is that the groove has at least one partwith complementary shape to said protrusion so that locking occurs in atangential direction when the groove is in contact with the protrusionon the wedge member.

FIG. 8 shows an alternative embodiment of the invention used for stackmembers where the slots 44 b for the cable windings have a profilesimilar to a bicycle chain so that each cable part (in the Figuresymbolised by a small circle) is situated in a wider part of the slot,and these parts are separated by narrower waist parts.

The invention is not limited to the embodiments shown. Severalmodifications are feasible within the scope of the invention.

What is claimed is:
 1. A laminated magnetic core for rotating electricmachines, wherein said laminated magnetic core comprises: a number ofstack members each including a number of sheets of metal joinedtogether, each stack member having a pair of identical grooves ofselected cross-sectional area; wedge members of selected cross-sectionalarea including a maximum width dimension arranged to cooperate with thegrooves to join said stack members together, wherein the cross-sectionalarea of the groove is larger than the cross-sectional area of the wedgemember, and the grooves each have an entrance larger than the maximumwidth dimension of the cross section of the wedge member, the wedgemember including a pair of two protrusions arranged symmetrically inrelation to a longitudinal axis of the wedge member, said groove havingat least one portion shaped to fit said protrusion, the stack members inthe laminated magnetic core being stacked on and partially overlappingeach other to form different layers of stack members, the grooves in thestack members in the various layers being arranged substantiallyopposite each other with the wedge members arranged in the grooves witha protrusion abutting the complementary shape of the groove in such amanner that the stack members in one layer are secured counter-clockwisein tangential direction and that the stack members in at least one ofthe adjacent layers are secured clockwise in tangential direction, andthe laminated magnetic core includes locking members arranged at leastat a transition between layers secured clockwise and layers securedcounter-clockwise in order to prevent tangential movement between thedifferent layers.
 2. A laminated magnetic core as claimed in claim 1,wherein at least one part of each groove has a shape complementary tothe protrusion of the wedge member located on the same side of thegrooves in each stack member.
 3. A laminated magnetic core as claimed inclaim 2, wherein the wedge member has dovetail-shaped cross section. 4.A laminated magnetic core as claimed in claim 3, wherein the crosssection of the groove has a trapezoidal shape in which one part has ashape complementary to said dovetail shape and one part has arectangular shape.
 5. A laminated magnetic core as claimed in claim 1,wherein the stack members in the various layers are arranged in such amanner that the stack members in one layer are mirror-inverted inrelation to the stack members in at least one of the adjacent layers. 6.A laminated magnetic core as claimed in claim 5, wherein each groove hasdovetail-shaped cross section.
 7. A laminated magnetic core as claimedin claim 1, wherein said locking device comprises spot welds beingarranged so that each stack member is joined by spot welds to layeradjacent thereto.
 8. A laminated magnetic core as claimed in claim 1,wherein said locking means comprises a linear weld that joins adjacentlayers of stack members with each other.
 9. A laminated magnetic core asclaimed in claim 1, wherein each stack member comprises an equal numberof metal sheets.
 10. A laminated magnetic core as claimed in claim 9,wherein the number of sheets is between 50 and 100 sheets.
 11. Alaminated magnetic core as claimed in claim 1, wherein the machineincludes a winding in the form of a high voltage field confining cable.12. A laminated magnetic core as claimed in claim 11, wherein the cablecomprises a conductive member, a first layer having semiconductingproperties in contact with and surrounding the conductive member; asolid insulating layer in contact with and surrounding the first layer;and a second layer having semiconducting properties in contact with andsurrounding the insulating layer.